Effects Of Flow Characteristics On The Performance Of Heat Transfer And Tube Vibration In Heat Exchangers With Helical Baffles

Shell-and-tube heat exchangers contribute to many industrial areas. However the major drawbacks still remain: large pressure drop, dead zone behind each segment baffle which results in fouling resistance and decrease of heat transfer rate, high risk of vibration failure on tube bundle. Helical baffles can help in alleviating the principal shortcomings of the conventional design by changing flow path of the shell side.In this paper, heat exchangers with helical baffles are analyzed by numerical simulation and experimental verification. Firstly, the influence of helix angle and overlapped space on the flow resistance and heat transfer characteristics of heat exchanger with helical baffles are analyzed through numerical simulation; Secondly, triple helical baffle heat exchangers in which more baffles can be arranged are proposed to enhance heat transfer rate in heat exchanger with large helix angle; Finally, the vibration performance of fluid obliquely across single tube and vortex shedding caused by fluid are analyzed.The results showed that:(1) Heat transfer coefficient and pressure drop decreased with the increasing of helix angle, and heat transfer coefficient per pressure drop increased with the increasing of helix angle.(2) The heat transfer rate and pressure drop of triple helical baffle heat exchanger are 27.9% higher and 42.3% higher than single helical baffle heat exchanger. Considering comprehensive heat transfer and flow resistance performance, the j/f1/3 of the triple helical design is 13.67% higher than single helical design.(3) Entransy dissipation rate caused by heat transfer was calculated by T-Q method. The variation trend is similar to heat transfer coefficient, larger helix angle leads to lower entransy dissipation rate and larger Re number leads to higher entransy dissipation rate.(4) Vortex shedding frequency decreased first then increased when longitudinal flow changed into cross flow, the minimum frequency occurred when helix angle falls between 40°~50°.Lift coefficient increased with the increasing of helix angle.